After 20 years of development, energy density of a lithium ion battery has been significantly improved. At present, the energy density of a lithium ion battery has been developed to a bottleneck stage. Increasing the charging speed of a lithium ion battery with limited energy density can enhance user's experience. Therefore, lithium ion battery having high energy density which can be charged quickly will stand out in the future competition.
In charging process of a lithium ion battery, lithium precipitation only occurs at the anode when the anode potential is reduced to a certain over potential for a certain period of time. This potential is the lowest anode potential of at which no lithium precipitation at the anode, usually expressed by η. The existing method for charging a lithium ion battery usually includes charging the lithium ion battery at a constant current to a potential and then charging the lithium ion battery at a constant voltage at this potential. The existing method for charging a lithium ion battery may lead to increase of the cathode potential of the lithium ion battery and reduce of the anode potential of the lithium ion battery. When the anode potential is below 0V, the lithium ion will be reduced to lithium via precipitation at the surface of the anode. Especially in low temperature conditions, due to the decline of ion and electronic conductivity of the lithium ion battery, the charging process will cause increased polarization. A continuous charging will make the polarization more obvious and increase the possibility of lithium precipitation. The precipitation of lithium dendrite will be accumulated in the electrode surface, which threatens to the safety performance of lithium ion battery seriously.
For a lithium ion battery, the safe charging region is certain, i.e. there is a maximum rate at which no lithium precipitation occurs at the anode. When the charging rate is higher than the maximum rate, lithium precipitation occurs at the anode, thereby affecting the safety performance and service life of lithium ion battery. In order to improve charging speed of the lithium ion battery, charging method can be optimized to inhibit lithium precipitation at the at high large rate, thereby expanding its safe charging range and improving the maximum charging rate of the anode at which no lithium precipitation occurs.
In view of the foregoing, what is needed, therefore, is to provide a method for charging a lithium ion battery which can inhibit lithium precipitation at the anode, so as to improve safe charging rate, safety performance and cycle life of the lithium ion battery.